Accordion Portrait

Here is how to do it on PS.

Open PS, make a new blank document that is 8in heigh x 12 in long, 300 ppi.

Show your ruler (Command and R) and your "snap-to guides". You can add these by dragging them from the left side of the document.

Add a vertical guide for every inch on the page.

Pick 2 images to show on either side.

You will have to "cut and paste" your image into "slices" on the PS document.

Select your first image.

Using the rectangular selection tool, select a 1 inch vertical "strip" of the image.

Push command and J to duplicate that "slice".

Repeat this for each 1 inch "slice".

You should now have every "slice" of your image on  separate layers.

Turn off the eyeball for your image layer.

Move every "slice" of the image so there is a 1 inch gap between each part of the image.

Place all of those layers in one folder.

Repeat the previous steps on the second image.

Your final should look like the image shown below, with each "slice" swapping back and forth between the 2 images.